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Date: Tue, 18 Aug 2020 11:58:49 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Michal Hocko <mhocko@...e.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
David Hildenbrand <david@...hat.com>,
Dan Williams <dan.j.williams@...el.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hotplug: Enumerate memory range offlining failure
reasons
On 08/18/2020 11:35 AM, Michal Hocko wrote:
> On Tue 18-08-20 09:52:02, Anshuman Khandual wrote:
>> Currently a debug message is printed describing the reason for memory range
>> offline failure. This just enumerates existing reason codes which improves
>> overall readability and makes it cleaner. This does not add any functional
>> change.
>
> Wasn't something like that posted already? To be honest I do not think
There was a similar one regarding bad page reason.
https://patchwork.kernel.org/patch/11464713/
> this is worth the additional LOC. We are talking about few strings used
> at a single place. I really do not see any simplification, constants are
> sometimes even longer than the strings they are describing.
I am still trying to understand why enumerating all potential offline
failure reasons in a single place (i.e via enum) is not a better idea
than strings scattered across the function. Besides being cleaner, it
classifies, organizes and provide a structure to the set of reasons.
It is not just about string replacement with constants.
>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Michal Hocko <mhocko@...e.com>
>> Cc: Dan Williams <dan.j.williams@...el.com>
>> Cc: linux-mm@...ck.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>> This is based on 5.9-rc1
>>
>> include/linux/memory.h | 28 ++++++++++++++++++++++++++++
>> mm/memory_hotplug.c | 18 +++++++++---------
>> 2 files changed, 37 insertions(+), 9 deletions(-)
>>
>> diff --git a/include/linux/memory.h b/include/linux/memory.h
>> index 439a89e758d8..4b52d706edc1 100644
>> --- a/include/linux/memory.h
>> +++ b/include/linux/memory.h
>> @@ -44,6 +44,34 @@ int set_memory_block_size_order(unsigned int order);
>> #define MEM_CANCEL_ONLINE (1<<4)
>> #define MEM_CANCEL_OFFLINE (1<<5)
>>
>> +/*
>> + * Memory offline failure reasons
>> + */
>> +enum offline_failure_reason {
>> + OFFLINE_FAILURE_MEMHOLES,
>> + OFFLINE_FAILURE_MULTIZONE,
>> + OFFLINE_FAILURE_ISOLATE,
>> + OFFLINE_FAILURE_NOTIFIER,
>> + OFFLINE_FAILURE_SIGNAL,
>> + OFFLINE_FAILURE_UNMOVABLE,
>> + OFFLINE_FAILURE_DISSOLVE,
>> +};
>> +
>> +static const char *const offline_failure_names[] = {
>> + [OFFLINE_FAILURE_MEMHOLES] = "memory holes",
>> + [OFFLINE_FAILURE_MULTIZONE] = "multizone range",
>> + [OFFLINE_FAILURE_ISOLATE] = "failure to isolate range",
>> + [OFFLINE_FAILURE_NOTIFIER] = "notifier failure",
>> + [OFFLINE_FAILURE_SIGNAL] = "signal backoff",
>> + [OFFLINE_FAILURE_UNMOVABLE] = "unmovable page",
>> + [OFFLINE_FAILURE_DISSOLVE] = "failure to dissolve huge pages",
>> +};
>> +
>> +static inline const char *offline_failure(enum offline_failure_reason reason)
>> +{
>> + return offline_failure_names[reason];
>> +}
>> +
>> struct memory_notify {
>> unsigned long start_pfn;
>> unsigned long nr_pages;
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index e9d5ab5d3ca0..b3fa36a09d7f 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1484,7 +1484,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> unsigned long flags;
>> struct zone *zone;
>> struct memory_notify arg;
>> - char *reason;
>> + enum offline_failure_reason reason;
>>
>> mem_hotplug_begin();
>>
>> @@ -1500,7 +1500,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> count_system_ram_pages_cb);
>> if (nr_pages != end_pfn - start_pfn) {
>> ret = -EINVAL;
>> - reason = "memory holes";
>> + reason = OFFLINE_FAILURE_MEMHOLES;
>> goto failed_removal;
>> }
>>
>> @@ -1509,7 +1509,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> zone = test_pages_in_a_zone(start_pfn, end_pfn);
>> if (!zone) {
>> ret = -EINVAL;
>> - reason = "multizone range";
>> + reason = OFFLINE_FAILURE_MULTIZONE;
>> goto failed_removal;
>> }
>> node = zone_to_nid(zone);
>> @@ -1519,7 +1519,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> MIGRATE_MOVABLE,
>> MEMORY_OFFLINE | REPORT_FAILURE);
>> if (ret < 0) {
>> - reason = "failure to isolate range";
>> + reason = OFFLINE_FAILURE_ISOLATE;
>> goto failed_removal;
>> }
>> nr_isolate_pageblock = ret;
>> @@ -1531,7 +1531,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> ret = memory_notify(MEM_GOING_OFFLINE, &arg);
>> ret = notifier_to_errno(ret);
>> if (ret) {
>> - reason = "notifier failure";
>> + reason = OFFLINE_FAILURE_NOTIFIER;
>> goto failed_removal_isolated;
>> }
>>
>> @@ -1540,7 +1540,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> do {
>> if (signal_pending(current)) {
>> ret = -EINTR;
>> - reason = "signal backoff";
>> + reason = OFFLINE_FAILURE_SIGNAL;
>> goto failed_removal_isolated;
>> }
>>
>> @@ -1558,7 +1558,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> } while (!ret);
>>
>> if (ret != -ENOENT) {
>> - reason = "unmovable page";
>> + reason = OFFLINE_FAILURE_UNMOVABLE;
>> goto failed_removal_isolated;
>> }
>>
>> @@ -1569,7 +1569,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> */
>> ret = dissolve_free_huge_pages(start_pfn, end_pfn);
>> if (ret) {
>> - reason = "failure to dissolve huge pages";
>> + reason = OFFLINE_FAILURE_DISSOLVE;
>> goto failed_removal_isolated;
>> }
>> /* check again */
>> @@ -1627,7 +1627,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>> pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to %s\n",
>> (unsigned long long) start_pfn << PAGE_SHIFT,
>> ((unsigned long long) end_pfn << PAGE_SHIFT) - 1,
>> - reason);
>> + offline_failure(reason));
>> /* pushback to free area */
>> mem_hotplug_done();
>> return ret;
>> --
>> 2.20.1
>>
>
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